In conventional optical systems, such as in digital cameras, motors and solenoids are used as sources of power to displace gears and cams which act upon optical elements, e.g., lenses, to provide focusing, zoom, and shake prevention. There are many disadvantages to such conventional systems—power consumption is high, response times are long, accuracy is limited and space requirements are high.
Advancements in miniaturized technologies have led to high-quality, highly-functioning, light-weight portable devices, and an ever-increasing consumer demand for even further improvements. An example of this is the development of cellular telephones to include a camera, often referred to as camera phones. While the majority of such camera phones employ an all-mechanical lens module having a small form factor lens, this approach does not offer variable or auto-focusing and zoom capabilities due to the significant number of moving parts required. For example, zoom capability requires a combination of lens elements, a motor, and a cam mechanism for transmitting the rotational movement of the motor to linear movement in order to adjust the relative positions of the lenses and an associated image sensor in order to obtain the desired magnification. In addition to the motor and cam mechanism, a plurality of reduction gears are is used to accurately control the relative positioning of the lenses.
Thus, while variable focusing and zoom features are possible within a camera phone and other optical systems having a relatively small form factor, these features would add substantially to the overall mass of these devices. Further, due to the necessity of an extensive number of moving components, power consumption is significantly high and manufacturing costs are increased.
Another approach which reduces the number of parts and mass of an optical system involves the use of a liquid lens to provide variable focusing and zoom capabilities. With such liquid lens systems, the volume of the fluid in the lens may be varied to adjust the focal length of the lens. This adjustment can be done without moving the lens, thus it is possible to realize zoom and variable focusing functions without a motor and cam mechanism.
One type of liquid lens system involves the pumping of liquid into and out of a lens chamber to change the curvature of an elastic membrane surface which defines at least a portion of the lens chamber. The transfer of fluid into and out of the lens chamber may be accomplished strictly by mechanical means, as described in U.S. Pat. Nos. 5,684,637 and 6,715,876 and U.S. Patent Application Publication No. 2007/0030573 (see, e.g., the embodiment of FIGS. 6A-6C in the latter patent document). For these types of lens systems, a complicated control system is usually needed. Such a control system involves additional moving components to pump and evacuate fluid into the lens chamber, making these types of lens systems bulky, expensive and sensitive to vibration. Another variation of such a liquid lens system is described in U.S. Patent Application Publication No. 2007/0030573. This system involves the pumping of fluid in and out of a lens chamber having a compliant membrane, the fluid movement of which is accomplished by electromechanical means (see, e.g., the embodiment of FIGS. 7-9C of that patent document). While the use of an electromechanical actuator may reduce the number of components required for the liquid lens system, by requiring the use of a liquid reservoir in addition to the liquid chamber which defines the lens, the bulkiness and mass of the system remain less than desirable.
Rather than changing the volume of liquid within a lens to effect a change in its shape, another type of liquid lens employs a fixed volume of liquid. One example of such a system is disclosed in U.S. Patent Application Publication No. 2006/0164731 in which a sealed liquid lens is attached about its periphery to an impeller structure which imparts movement and pressure to the fluid filled lens. The impeller structure is made of a number of movable thin plates fastened at regular intervals around the lens. The impeller can be operated mechanically or electro-mechanically to change the diameter of the lens which, in turn, results in a change in radius of the optical surface of the liquid lens. While the size of the lens system may be reduced by the elimination of an additional liquid reservoir, the number of moving parts required of such an impeller mechanism adds mass to the system and presents reliability issues.
Other variable-focus liquid lens systems utilizing a fixed volume of fluid are known which employ electrowetting principles. Two producers of liquid lenses, Varioptic of France and Philips Electronics of the Netherlands, have developed such a lens system which employs two immiscible (non-mixing) liquids, one an electrically conductive solution and the other a non-conductive fluid, having different refractive indices. With the operative placement of electrodes, a voltage applied thereto modifies the curvature of the interface between the liquids. More specifically, by modulating the electric field across the interface, its surface tension is caused to change thereby altering its radius of curvature and focusing light rays passing therethrough to either a greater or lesser extent. In other words, the shape of the lens can be made to transition between convergent (concave) and divergent (convex) states and back again. Changing the shape of the lens changes the curvature radius of the lens, allowing the focal length to be changed freely. Examples of such liquid lenses are disclosed in U.S. Pat. No. 6,369,954 and U.S. Patent Application Publication Nos. 2006/0126190, 2006/0152814 and 2007/0002455. While providing a reduced form factor over the all-mechanical lens positioners, these types of liquid lens systems have significant drawbacks. Typically, the voltage required to effect the desired focal change upon the liquid lens is very high (>250 volts). This results in relatively high power consumption which in turn reduces the potential life of the battery used or, alternatively, requires a larger battery. Further, as this type of lens structure requires the use of two liquids, it is fairly complicated and expensive to construct.
Accordingly, it would be advantageous to provide an optical lens system which overcomes the limitations of the prior art. It would be particularly advantageous to provide such a system whereby the arrangement of and the mechanical interface between a fluidic or liquid lens and its actuator structure were highly integrated so as to reduce the form factor as much as possible. It would be greatly beneficial if such an optical system involved a minimal number of mechanical components, thereby reducing the complexity and fabrication costs of the system. Additionally, it would be highly desirable if such a system could effect a relatively large change in the optical properties of its liquid lens while requiring a relatively small work load, i.e., movement or stroke, on the part of the lens actuator.